German Tax ID
Validator
Check whether a German Tax ID (Steuer-IdNr) is correctly formatted and passes the official ISO/IEC 7064 Mod 11,10 checksum — entirely in your browser.
About German Tax ID (Steuer-IdNr) Validation
The German Tax ID (Steueridentifikationsnummer or Steuer-ID) is the unique, permanent 11-digit fiscal identifier assigned to every resident in Germany.
It consists of 11 numerical digits, where the first digit is non-zero and the 11th digit is a checksum computed according to ISO 7064 Modulo 11, 10 (DIN 5007-1).
Anatomy & Structure of German IdNr
| Position | Field | Length | Meaning & Rule | Example |
|---|---|---|---|---|
| 1 to 10 | Base Number | 10 digits | Sequential base where first digit is never 0 and exactly one digit appears twice | 1234567890 |
| 11 | Check Digit | 1 digit | Control digit calculated according to ISO/IEC 7064, Mod 11, 10 standard | 4 |
IdNr Validation Algorithm (ISO/IEC 7064, Mod 11, 10)
| Step | Description |
|---|---|
| 1. Initialize the product | Initialize the accumulated product variable with base value P = 10. |
| 2. Sum each digit | For each of the first 10 digits: compute sum S = (digit + P) % 10. If S is 0, reset S = 10. |
| 3. Update the product | Update product: P = (S × 2) % 11. |
| 4. Compute the check digit candidate | Compute check digit candidate: C = 11 − P. If C is 10, the check digit is 0; otherwise, it equals C. |
| 5. Compare with the 11th digit | Compare with the 11th digit to confirm mathematical validity. |
Frequently Asked Questions & Technical Guidelines
What is the difference between Steuer-IdNr and Steuernummer in Germany?
The Steuer-IdNr is a permanent, lifelong 11-digit number assigned once to every resident and used for all dealings with German tax authorities. The Steuernummer is a separate, non-permanent number assigned by the local tax office (Finanzamt) to a specific tax matter — it changes if you move, switch tax offices, or start a business, and is used mainly on tax returns and invoices.
Are the data in this tool real or official?
No. This validator only checks whether a number satisfies the ISO/IEC 7064 Mod 11,10 checksum used by the Steuer-IdNr format — it does not look up or confirm any real taxpayer record with the BZSt. A result of "valid" means the number is mathematically well-formed, not that it belongs to a real person.